1. Field of the Invention
The present invention relates to a wide viewing angle polarizing plate capable of forming a liquid crystal display which causes less brightness unevenness by heat history, thereby exhibiting good visibility in a wide viewing angle range.
2. Description of the Background Art
Hitherto, a wide viewing angle polarizing plate has been known in which a compensating plate obtained by supporting a compensating layer with a cellulose triacetate film is bonded as a transparent protective layer of a polarizing film. Such a wide viewing angle polarizing plate is applied to a liquid crystal cell to form a liquid crystal display (LCD) exhibiting a good visibility at a wide viewing angle. Since it is a key device of an LCD, it is used in a state in which an adhesive layer made of an acryl series adhesive or the like for bonding it to the liquid crystal cell is attached in advance for the purpose of preventing the variation of quality and providing a more efficient assembling process, and in which a brightness enhanced plate or a retardation plate is laminated via an adhesive layer for the purpose of improving the brightness and further adjusting the retardation.
However, when such a wide viewing angle polarizing plate is bonded onto a liquid crystal cell via an adhesive layer and heated, it causes a problem of generation of brightness unevenness. This brightness unevenness typically appears in a window frame shape, and increases further when a brightness enhanced plate or a retardation plate is laminated.
Thus, an object of the present invention is develop a wide viewing angle polarizing plate capable of forming a liquid crystal display which causes less brightness unevenness by heat history, thereby exhibiting good visibility at a wide viewing angle.
The present invention provides a wide viewing angle polarizing plate comprising a polarizing plate in which a transparent protective layer made of an compensating plate is provided on at least one surface of a polarizing film; one or both of a brightness enhanced plate and a retardation plate laminated on the polarizing plate via an adhesive layer thereby to form a laminate; and an adhesive layer disposed on one surface or on both surfaces of an outer surface of the laminate, wherein the adhesive layers all have a 1000% modulus at 90xc2x0 C. of at most 6 g/mm2.
The present invention in the above-mentioned wide viewing angle polarizing plate, the compensating plate is a liquid crystal layer supported by a film.
The present invention in the above-mentioned wide viewing angle polarizing plate, the polarizing plate is provided in such a manner as to be disposed between the brightness enhanced plate and the adhesive layer on the outer surface.
The present invention in the above-mentioned wide viewing angle polarizing plate, the retardation plate is provided in such a manner as to be disposed between the polarizing plate and the adhesive layer on the outer surface.
The present invention in the above-mentioned wide viewing angle polarizing plate, the adhesive layer provided on the outer surface of the laminate has a larger thickness than the adhesive layer disposed inside the laminate.
Also, the present invention provides a liquid crystal display having the above-mentioned wide viewing angle polarizing plate on at least one side of a liquid crystal cell.
The inventors of the present invention repeatedly made eager studies in order to solve the aforementioned problem of brightness unevenness, and found out that such generation of brightness unevenness is caused by change in retardation and the residual of this state owing to generation of stress brought about by contraction or the like of the compensating plate or the like when it is heated. By bonding via the aforesaid adhesive layer, the stress generated at the time of heating can be relaxed, and the generation of brightness unevenness can be prevented. With the use of this wide viewing angle polarizing plate, a high-quality and good-durability liquid crystal display having a good visibility and being excellent in viewing angle can be obtained.